ML20117Q052
Text
1 September 10, 1990 Docket Nos. 50-317 and 50-318 3
MEMORANDUM FOR: Robert A. Capra, Director Project Directorate I-1 Division of Reactor Projects I/II FROM:
Conrad E. McCracken, Chief Plant Systems Branch Division of Systems Technology
SUBJECT:
CALVERT CLIFFS, UNITS 1 AND 2 LER FOLLOWUP RELATED TO POTENTIAL LOSS OF SERVICE WATER DUE TO PIPE BREAK Our August 31, 1990 memorandum transmitted our safety evaluation on the same subject as this memorandum.
In that memorandum, we indicated our intent to address the licensee's interpretation of the licensing basis for the plant as a separate issue from ti.e safety evaluation. This memorandum addresses that issue.
In Supplement No. I to LER 89-023 dated March 12, 1990, tne licensee concluded that the identified design deficiency was outside the r,rigin01 licensing design basis for the service water system (SWS) at Calvert Cl3ffs, Units 1 and 2.
The licensee's conclusion was based on the fact that the spcific scenario of concern (seismic event coupled with a loss of offsite power) was not identified in the staff's 1972 Safety Evaluation Report (SER).
We do not agree with the licensee's conclusions related to the design basis for the SWS. The licensee's reference only to the staff's 1972 SER is inappropriate. The staff's 5 F is not the sole licensing basis for a plant.
The staff's SERs never describe all of the scenarios that make up the design basis for any system.
In the case of the Calvert Cliffs SWS, the SER t
described what was the worst case design basis accident, f.e., a loss of coolant accident (LOCA) with a simultaneous loss of offsite power (LOOP).
This design basis worst case accident is presumed to place the most heat load demand on the SWS. The scenario of concern, a seismic event coupled with a LOOP is not considered an " accident" and is, therefore, not addressed as a Chapter 15 (Chapter 14 for Calvert Cliffs) event. However, the overall response of a plant and its systems to a seismic event coupled with a single active failure is evaluated by the staff. This is generally done on a system by system evaluation. As part of this evaluation, it is assumed that a LOOP occurs because the offsite power system is not designed to seismic Category I requirements.
In the case of Calvert Cliffs, the drawings in the Final Safety Analysis Report (FSAR) indicate that the air-operated isolation valves which isolate the nonseismic portion of the SWS are fail closed valves. Therefore, an assumption that these valves fail closed on loss of air and/or power would have been made by the staff during its review.
If in fact, they did fail 2
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closed on a LOOP, the system would be able to perfom its safety function (assuming an adequate closure time) following a combined seismic event, LOOP i
and single active failure.
l The staff's SER is based on the design details provided in the licensee's FSAR which basically provides the licensing basis for the plant.
In Section 8.4.1.2 I
of the licensee's FSAR, it is stated that "the emergency diesel generators and their auxiliaries are designed to withstand Seismic Category I accelerations i
and are installed in Category I structures." This statement appears to i
indicate that a loss of offsite power is assumed in a seismic event.
Additionally, the SWS is required to meet General Design Criterion (GDC) 2
" Design Basis for Protection Against Natural Phenomena." GDC 2 requires that systems important to stfety be designed to withstand the effects of earthquakes with a design basis that reflects " appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena. " This is interpreted to include a loss of offsite as "an
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appropriate combination" given that the offsite power system is not designed to seismic Category I requirements.
We are sending you this memorandum to identify our position (as it differs from the licensee's) regarding the licensing basis for the SWS at Calvert Cliffs. You may want to notify Region I of our position regarding the ifcensee's interpretation of the licensing basis for the Calvert Cliffs SWS for future communications with the licensee. You may also want to infom the licensee in order to avoid similar problems related to the plant licensing l
basis in the future.
3 l
George Hub fr Conrad E. McCracken, Chief Plant Systems Branch y
Division of Systems Technology cc:
P. W. Baranowsky DISTRIBUTION i
D. G. Mcdonald Docket File C. E. Rossi Plant File A. P. Young JKudrick M. L. Reardon RArchitzel GHubbard l
CONTACT:
W. LeFaye JLyons x23285 WLeFcve y:
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